#!/usr/bin/env python3
n, c = [int(i) for i in input().split()]
a = [int(i) for i in input().split()]
best = (9e9,0)
current = 0
for i,v in enumerate(a):
    current = max(current+v-c,0)
    if current < (n-i)*c:
        best = min(best,(current,i+1))
print(best[1]-1 if best[1] else "impossible")